The inspection of the crown ring of a container is important for a number of reasons, which include integrity of the crown ring to provide a proper seal, adequate surface area so the crown cap will seat properly, and avoidance of damage to the crown ring when the cap is removed.
Prior apparatus has included means for subjecting the crown ring to light beams on either the inside or outside and cooperating opposed detection means which is energized if a chip defect is present. Such apparatus has required rotating the inspection means or the container while interrupting the conveyance of the containers during the inspection period. Interrupting container movement is necessary when a part of the inspection apparatus must be inserted even partly into the container mouth.
Certain prior apparatus has effected container rim inspection by directing a beam of radiant energy of a polarized character so that the beam is given an electric vector perpendicular to the plane of incidence, and rotating the container to achieve the desired scan. Another type of inspection apparatus has relied upon illuminating the crown ring and looking at the illuminated crown ring through a rotating prism device, all without interfering with the high speed movement of the containers.